Not knowing your location, I can tell you what I did.
Here in Coronado, just across the bay from San Diego, I bought a 5 KW electric unit heater from Amazon and mounted it to the ceiling in my garage, I ran a 30 Amp, 240 volt circuit to it. The heater is controlled by a mechanical twist timer and a 40 Amp relay, the 24 Volt coil voltage comes from a repurposed power supply from a sprinkler timer.
I used the twist timer to keep the heater from accidentally being left on when the shop is unoccupied.
I am aware that many members of the Garage Journal Community don’t enjoy the same weather as we do in Coronado.
The Solar System on the roof makes the electric power very inexpensive.